Limit switch



April 1937- O. F. CARLSON 2,078,441

LIMIT SWITCH Filed Nov. 16, 1955 2 Sheets-Sheet l fame/afar.- 050427 FCcz-rlson Patented Apr. 27, 1937 UNITED STATES LIMIT SWI'ECH Oscar F. Carlson, @hicago, ill, assignor to fiscal F. Carlson Company, Ghicago, 111., a corporation of Illinois Application Novcnilcer l6, i935, Serial No. ttl3l l5 cialma This invention relates to limit switches, and more particularly is directed to limit switches for use in connection with oil burners and similar oil utilizing devices employing a storage tank for 5 feeding oil to the burner equipment. However, the switch can be employed as a limit control for any type of fluid storage tank or pressure systen'i in which operation of the switch in response to changes in a pressure responsive element is ole= sired.

In my copending application, Serial No. 5,893, filed February 11, 1935, of which the present application is a continuation in part, i disclose a control switch of this type for indicating the lowering of level in an oil supply tank for a burner or the like The present invention is directed more particularly to a switch structure responsive to variations in pressure and capable of controlling a circuit or circuits in accordance with any desired pressure setting of a source of pressure to which the switch is connected. I

One of the primary objects of the present invention is to provide a pressure limit switch in which the circuit controlling member is positively snapped from pressure engagement with its comtacts out of engagement therewith, independently of the rate of expansion or contraction of the pressure responsive member.

Another object of the present invention is to provide a switch actuating member in which rate of movement can be varied as desired with respect to a predetermined rate of movement of a pressure responsive element.

Another object of the present invention is to 5 provide a motion transmitting lever pivoted at one end, having an adjustable tensioning means on the opposite end, with a pressure responsive member engaging one side of the lever intermediate its ends, and a switch actuating lever 40 having adjustable engagement with the opposite side of said lever, whereby the movement of the lever constitutes a differential between the spring tension and the pressure within the pressure re sponsive member, and is transmitted proportionateiy to the switch operating lever, depending:

upon the point of engagement of the latter with the motion transmitting lever.

Still another object of the present invention is to provide a sliclable contact carriage which may be moved into selected positions with respect to the switch operating mechanism to produce different rates of operation of the switch per unit operating movement of the operating mechanism.

Another feature of the present invention is the provision of a compact, simplifies. limit switch (Ella 260-83) which is capable of many calibrations for eflecting actuation of the switch at any desired pressures.

Still another feature of the present construc= tion is that the majority of the operating parts may be formed of metal stampings or the like, and may be quickly and readily assembled into position with a minimum of adjustment and labor.

A still further object of the present invention is the provision of a pressure responsive switch employing a leaf spring contact carrying member maintained slightly arched under longitudinal compression, actuation of the member being produced by exertion of force upon the spring normal to its longitudinal surface. This produces an endwise component of stress, increasing the normal longitudinal compression on the spring, and thereby producing abrupt lateral flexing of the spring intermediate its ends in the direction over center away from the force. One or more stationary contacts may he engaged by the spring, and provide abutments restraining its flexing movement, whereby a positive pressure contact is provided between the spring member and the contacts engaged thereby.

Another advantage secured by the present in vention is the provision of an insulating base member securing the contacts, the leaf spring contact and the external terminal lugs in position, which can be removed fromthe switch as a unit for inspection, repair, or replacement.

Other objects and advantages of the present invention will appear more fully from the following detailed. description, which, taken in connection with the accompanying drawings, will disclose to those skilled in the art the particular construction and operation of a preferred form of my present invention.

In the drawings:

Figure l is a vertical sectional view through a control limit switch oi the present design;

Figure 2 is an end sectional view, taken sub-= stantialiy on line 2-2 of Figure 1;

Figures 3 and l are front and top views, re= spectively, of the switch clamping plate;

Figure 5 is a front elevational view of the switch mounting bracket for carrying the switch assembly; and

Figure 6 is a perspective view of the leaf spring contactingmember.

Referring now in detail to the drawings, I provide a generally rectangular box-like housing iii having enlarged opening at its lower end adapted to receive the extending portion of a fitting 52 which at its lower end is threaded,

as indicated at l3, for connection to any suitable pressure supply line or the like. The fitting is mounted within the inner surface of the base of the housing i6 by means of a plurality of screw members l4, and upon its inner surface is provided with an annular shoulder portion l5 receiving the end l6 of a hollow flexible sylphon bellows member i1, which is sealed or otherwise suitably secured about the shoulder l5 to have pressure tight engagement therewith.

The upper end of the bellows I1 is provided with a closure plate II, to which the upper end flange of the bellows is sealed, the plate 16 carrying a depending reenforcing member l6 secured thereto by means of the rivet member 26, which is provided with a conical head portion 22 adapted to engage a pivoted lever 26 mounted upon the U-shaped bracket 24. The bracket 24 is provided with inturned ends 2! clamped beneath the lower flange portion of the fitting l2 by the screws l4, and includes a central slotted portion in the upper horizontal surface thereof. The bracket at one end is provided with the up struck ear members 26 forming a support for the pivot pin 26 upon which the lever 23 is pivoted.

The fitting I2 is provided with a laterally extending lug portion 21 which is adapted to receive the screw member 26 therein, this member serving as a. suitable support for the lower end of a compression spring member 29, which at its upper end is provided with the hooked portion 36 engaging over the crimped end 32 of the lever the conical head portion 22 of the rivet member 26, is provided with an upstruck portion 33 serving as a bearing seat for the conical head of the member 26. Extending longitudinally of the lever 23 are a pair of spaced rib members 34, which serve as stifiening means for the lever 23. The surface of the lever between the ribs 34 is adapted to receive the head portion 35 of the actuating bolt 36. The lever 23 is provided with upstruck cars 31 which have pivotal engagement about the pin 26 between the ears 25 of the bracket 24, as clearly shown in Figure 2.

Considering now the switch operating mechanism of the construction, I provide a switch mounting bracket 46, shown in more detail in Figure 5, having a plurality of normally extending ear portions 42 apertured to receive suitable rivet members 43 for securing the same to the rear wall of the housing l6. The bracket 46 comprises a substantially planar vertically extending portion 46, having the inturned tab portions 45 bent inwardly and rearwardly between the oppositely disposed horizontally extending arms 46 which space the channel portion 44 outwardly away from the rear wall of the housing 16. The front face of the bracket member 46 is provided with a pair of spaced slots 41 extending longitudinally thereof, and disposed upon opposite sides of the tab members 45.

Mounted within the channel portion of the bracket 46' is a sliding carrier member disclosed more in detail in Figures 3 and 4.- This member comprises a metal strip 56 having a longitudinal extent less than the extent of the bracket member 46, the strip being provided with upstruck bosses 52 adapted to have engagement within the slots 41 for guiding the member 56 for longitudinal sliding movement within the bracket.

The carrier member 66 is also provided with a pair of threaded openings 63 disposed adjacent the outer ends thereof, which openings are aligned with the slots 41 and are adapted to receive suitable screw members 64 which pass through and secure an insulating housing member or terminal block 56 to the carrier member 56 for conjoint sliding movement therewith.

The member 66 is provided with a central-normally extending rib portion 66 forming an insulating separation for the two terminal screws 61 and 66, these terminal screws passing through suitable terminal lugs 56 which are riveted, as by means of the rivets 66, to the normally extending able opening 62 is formed in the upper surface of .base portion of the housing member 66. A suitthe housing and serves as a means for passing an limits thereof. The contact 66 is somewhat resilient due to this type of mounting. Similarly the terminal screw 66, through its lug 56 and rivet 66',' 'is electrically connected with a bracket member 61 having the horizontally extending portion 66 carrying the contact 69. These two contacts are in the same horizontal plane, and are disposed in laterally spaced positions beneath the base of the housing 56. Preferably formed integral with the housing 66 and projecting downwardly from the base thereoi' are a pair of abutment stop members 16 which have their end faces lying in the same horizontal plane, and which are spaced directly above each of the contacts 66 and 69. a

It will be noted that the rivets 66 serve to support the terminal lugs in position upon the position projecting from the lower portion of the housing.

A suitable U-shaped bracket vmember 12 having outwardly extending ear portions 13 riveted, as indicated at 14, to the base of the housing, provides a depending hanger for receiving the pivot pin 15 engaging one end of the actuating lever 16 for pivotal movement thereabout. The actuating lever 16 is provided with longitudinally extending web portions providing stiffness for the membenand adjacent its outer end is provided with a suitable tapped opening 11 receiving the threaded portion of the screw member 36, this member 36 being locked in any desired adjusted position with respect to the lever 16 by means of the lock nut 18.

At its outer free end, the lever 16 is provided th an upturned end portion 19, having a pair of normally extending cars adapted to secure the insulating actuating plate 62 thereto. This plate 82 is provided with a recessed end forming a slot 63 adapted to receive the longitudinally extending portion of a leaf spring member 64 shown in more detail in Figure 6.

The spring member 64 is provided with a reversely curved thickened flat end portion 65 adapted to be anchored to the bottom face of the housing 55 by suitable lugs 66 formed integral with the bracket 61. The spring mem- III berjl is thus U-shaped and has the extending leg thereof disposed between the two brackets 64 and 61. Adjacent the opposite end of the terminal block the member 84 has a projecting tip portion passing through the supporting bracket 12 and having an extending end 86 engaged within a suitable slot formed in a resilient normally extending supporting member 81, which member is riveted to the base of the housing 55 by means of the rivet 88. The member 8! provides for longitudinal compression of the spring 84, serving to arch the same over center in opposite directions and maintaining the same under compression to provide for flexing thereof upon movement imparted thereto by the fork member 82. In its normal position the spring is arched outwardly away from the terminal block 55.

Intermediate its ends the spring member is provided with a laterally extending bridging member 89 which is clamped thereto as indicated at 99 and which, at its ends, is provided with contact portions 92 adapted to have pressure engagement with the contacts E6 and $9 when the spring is in the normal position shown in Figure 1. This provides'for bridging engagement between the contacts 66 and 39 to complete a circuit between the terminal screws i and 58.

In its opposite flexed position, the spring member 84 is moved over center to arch upwardly toward the terminal block, as viewed in Figure l, whereupon the ends of the bridging member 89 move into abutting engagement with the faces of the stop members 10, thereby retaining the spring in position against further movement and limiting its movement to an extent such that it tends to snap back into its normal position of contact engagement. There is some longitudinal movement of the spring as it moves over center, accommodated by the resilient support ill, whereby the contact portions 92 have wiping pressure engagement with contacts 36 and 69.

In the operation of the limit switch thus far described, pressure from any suitable pressure supply source is admitted through the fitting l2 into the interior of the bellows i'l. Increase of pressure results in expansion of the bellows, moving the conical head 22 of the rivet member 2'0 upwardly. This results in pivoting of the lever 23 about the pin 26, against the pressure of spring 29, and results in clockwise movement of this lever upwardly under the influence of the pressure within the bellows. The head end of the screw 35 is thus raised in position, irnparting a counter-clockwise movement to the lever it, whereby the insulating actuating mern ber 82, which engages the lateral surface of the spring member in a direction normal to its longitudinal extent, causes a flexing of the spring member at the point of engagement. Due to the fact that the spring is restrained tosome extent against longitudinal expansion by means of the support member til, the longitudinal COZ'llPlES sion of the spring is increased, and the spring snaps over center into abutting engagement with the stop members it, breaking the circuit be tween the contacts 66 and lid.

The spring will remain in this position until the pressure within the bellows ll decreases, whereupon, due to the resilience of the spring, the spring will force the lever iii downwardly, the head end 35 of the screw 35 following the movement of the lever 23 downwardly under cellapse of the bellows, and the spring will then snap heels over center into outwardly arched position and the contacts 92 will be forced into positive wiping pressure engagement with the contacts 66 and 89, reclosing the circuit through the terminal screws 51 and 58.

Due to the sliding movement of the member within the bracket 40, it is apparent that by loosening the screws 54 which clamp this memher in fixed position by clamping engagement be-- tween the housing and the face of the bracket member, the carrying member 50 may be moved longitudinally within the slots 41 to, move the entire contact assembly either to the right or left, as viewed in Figure 1. This results in corresponcling longitudinal movement of the head end 35 of the screw member 86 with respect to the upper surface of the lever 23, and thereby provides tor a diiferential ratio of movement being imparted to the lever l6, depending upon the point at which the head end 35 engages the lever 23. Thus, with the carriage moved to the extreme right-hand position, a considerably greater expansion of the bellows ill will be necessary in order to eiiect actuation of the switch, since the unit movement of the lever "it per unit movement of the lever 23 is decreased. Correspondingly, ii the switch contact carriage is moved to the extreme left-hand position, the movement of the bellows will produce a much greater unit movement of the lever ill to produce a quicker actuation of the contact spring, due to the fact that the unit movement of the lever lb is increased with respect to the unit movement of the lever 23. v

The adjustment of the tension on spring 29, which restrains the movement of the lever ,is produced by the screw member 28, and preferably this tension is adjusted at the factory, although of course it may be adjusted at the point of installation to provide a predetermined unit movement of the bellows per unit increase in pressure.

This loading of the bellows by the spring tension restrains the unit movement of lever 23 per unit increase of pressurein the bellows and also serves to bring lever 23 downwardly simultaneously with the collapse of the bellows, whereby spring M can snap over center to drop lever l6 into engagement with lever It will thus be apparent that l" have provided a limit switch in which the unit movement of the operating mechanism can be varied with respect the unit movement of the actuating mechanism, whereby the switch may be made to respond at various differentials of pressure, clependlng upon the point at which breaking and making of the circuit is desired.

As shown in Figure 2, 3 preferably provide a closure plate Elli which has, along its vertically attending edges, inwardly turned flanges provided with suitable openings @ll adapted to be snap over the bosses formed on the interior surface of the side walls of the housing ill. This provides at protecting shield for the switch contact structure and the bellows operating mechanism, and protects the same from accidental injury or the like. A suitable closure plate or cover for the'houslng is indicated at tilt and is provided with a peripheral flange portion Hi2 fitting over the defining edge portion of the faceof the l'loitsing ill. Suitable screws pas-shag through the threaded openings llllfi in the hosses are adapted secure the closure plate Mill in. position over the face of the housing iii. The ClOSillG pie e ltd may he provided with a central labor.

Having described my invention in accordance with the statutes, what I claim as new and desire to secure by Letters Patent is:

l.v A control switch comprising a housing, a

pressure responsive'jelement therein, meansfor introducing fluid-underpressure into the interior of said element, apair of spaced contacts, a contactor normally bridging between said contacts, means comprising a pair of spaced levers extending parallel to each other and to said contactor'and pivoted at opposite ends, one of said levers being actuated by said element to actuate the other of said levers in the opposite direction for snapping said contactor out of engagement with said contacts, said contactor having limited longitudinal movement to provide a wiping action across said contacts upon disengagement therefrom, and means for varying the amount of movement imparted by said one lever to said other lever upon unit movement of said one lever.

2. A control switch comprising a pressure responsive element, a leaf spring normally maintained in longitudinal compression and arched toward said element, a contact engaged by said spring. in its normal position, an insulated support for said spring, and means actuated by, expansion of said element, for moving said spring laterally out of normally arched position to snap said spring over center into oppositely arched f position, and means on said support for limiting over center movement of sa d spring whereby upon contraction of said element said spring snaps back into normal position, and means for varying the rate of movement of said snapping means with respect to the rate of expansion of said element.

3. A control switch comprising a leaf spring havingv a U-shaped end, insulating means anchoring one leg of said end, the opposite leg being extended, means resiliently abutting against tlze end of the extended leg whereby said leg is normally arched outwardly away from said anchored leg, 2. pair of contacts on one side of said leg and normally bridged by said spring, means for applying a-force to said extended leg intermediate its ends and normal to the surface thereof for snapping said leg over center into oppositely arched position; and means on said anchoring means limiting snap movement of said leg whereby said leg tends to return to normally arched position. 1

4. A control switch comprising a housing, an insulating terminal member carried thereby, terminal lugs carried by said member, a pair of laterally spaced contacts carried by said lugs Within said housing, a leaf spring normally arched into engagement with said contacts, means including a lever movable substantially normal to said spring, a second lever carried by said terminal member and having abutting engagement with said first lever, means carried by said second lever for snapping said spring over center out of contacting engagement, and means for shifting said terminal member in said housing to vary the point of abutting engagement between said levers.

5. In a control switch, a leaf spring member maintained in longitudinal compression and normally arched into circuit closing position, a lever pivoted adjacent one end of said spring and having abutting engagement therewith adiacent the oppositeend thereof, a pressure responsive element, a second lever parallel to said first lever and pivoted at its opposite end, said second lever being movable in response to movement of said element, means for transmitting movement of said second lever to' said first lever for snapping said spring ove'reenter out of circuit closing position, and means forshifting one of said levers longitudinally with respect tothe other of said levers for varying the movement imparted to said first lever by said second lever per unit movement of said element.

6.' Ina control switch, an insulating terminal member, aleaf spring carried thereby and maintainedfin longitudinal compression, a contact normally engaged by an intermediate portion ofsaid spring, and actuating means for snapping saidspring over center out of contact engagement comprising a pressure responsive element, a lever pivoted at one side thereof and movable in response to movement of said pressure responsive element, means carried by said terminal 7 member for transmitting movement of said lever to said spring, and means for varying the unit movement transmitted to said spring per unit movement of said element.

'7. In a control switch having a leaf spring contactor maintained under longitudinal compression and normally flexed into arched contact engaging position, actuating means for moving said contactor into oppositely flexed position comprising a pressure responsive bellows, a lever pivoted at one end and extending over said bellows in abutting engagement therewith, spring means engaging the opposite end of said lever for restraining movement of said lever upon expansion of said bellowsfa second pivoted lever for transmitting movement of said first lever to said contactor, and means for varying the increment of movement of said second lever per increment of movement of said first lever.

8. Actuating means for a leaf spring contactor type switch in which the spring is normally arched into contact engagement, comprising a pressure responsive element, means for restraining expansion of said element under increase in pressure, pivotally mounted motion transmitting means between said element and said spring for applying a force normal to the longitudinal arch of said spring to snap said spring over center out of contact engagement, and means for varying the rate of transmission of motion through said motion transmitting means.

9. In combination, a housing, a supporting bracket secured therein, a slide carried by said bracket and having longitudinal movement therein, a terminal block, means securing said block to said slide and adapted to clamp said slide in selected positions, a pair of contacts carried by said block, a leaf spring contactor normally arched into engagement with said contacts, actuating means including a pressure responsive bellows and motion transmitting means operated thereby for snapping said contactor over center out of contact engagement, and abutnients on said block for limiting snap movev.ried by said contactor intermediate its ends and ment of said contactor whereby said contactor tends to return to normally arched position.

10. In combination, a housing, a supporting bracket secured therein, a slide carried by said bracket and having longitudinal movement therein, a terminal block, means securing said block to said slide and adapted to clamp said slide in selected positions, a pair of contacts carried by' said block, a leaf spring contactor normally arched into engagement with said contacts, actuating means including a pressure responsive bellows and motion transmitting means operated thereby for snapping said contactor over center out of contact engagement, said motion transmitting means including a pivoted le ver carried by said block whereby upon longitudinal movement of said slide the ratio of movement between said bellows and said lever is varied.

11. In combination, a housing, a supporting bracket secured therein, a slide carried by said bracket and having longitudinal movement therein, a terminal block, means securing said block to said slide and adapted to clamp said slide in selected positions, a pair of contacts carried by said block, a leaf spring contactor normally arched into engagement with said con tacts, actuating means carried by said housing including a pressure responsive bellows and a lever movable in accordance with movement of said bellows, and a pivoted lever carried by said block and engageable with said first lever for transmitting movement of said bellows to said contactor to snap said contactor out of contact engagement, longitudinal adjustment of said slide varying the transmission of movement to said second lever per unit movement of said bellows.

12. The combination with a pair of contacts and a pressure responsive element for opening and closing the circuit therebetween, of a leaf spring contactor anchored at one end and having resilient means at the opposite end thereof for maintaining said contactor in longitudinal compression and normally arched over center in one direction, a, contact bridging member carnormally engaged with said contacts, means responsive to expansion of said element for exerting a force on said contactor normal to its longitudinal extent to snap said contactor over center, and means in said force exerting means for varying the ratio between movement of said element and movement of said contactor.

13. A control switch including a pair of contacts, contactor means normally bridging said contacts, a pressure responsive element, a lever pivoted at one side of said element and extending over said element to the opposite side thereof, spring means engaging the free end of said lever and urging said lever downwardly on said element, means on said element for rotating Said lever upwardly against said spring means, a second lever pivoted above said free end of said first lever and having point contact adjacent its free end with the surface of said first lever, means on said second lever for moving said contactor means out of contact engagement, and means for shifting said second lever longitudinally to vary the point contact engagement between said levers.

14. In combination, a supporting member, a switch carrier having adjustablesliding engagement therewith, a pressure responsive element movable normal to said carrier, a pair of parallelly extending levers, one pivoted at one end on one side of said element and the other pivotedat its opposite end to said carrier on the opposite side of said element, a contactor carried by said carrier and extending substantially parallel to said levers, and means for transmitting motion of said element through said levers to said contactor, said carrier being adjustable to vary the ratio of movement transmitted to said contactor through said levers per unit movement of said element.

15. A switch housing having a slide support fixed therein, a switch carrier on said support including a resilient contactor and a pivoted lever, said lever extending parallel to said contactor and having abutting engagement therewith at its free end, a second lever extending parallel to said first lever and spaced therefrom, said second lever being pivotally mounted adjacent the free end of said first lever,.means providing abutting engagement therebetween intermediate the ends of said levers, and means for shifting said carrier on said support to vary the point of engagement of said first lever with respect to the second lever for modifying the transmission of movement from said second lever to said first lever.

OSCAR F. CARLSON. 

